How can I completely remove Blender from my Mac?
Check the OSX sections in the Blender manual, it lists all the default paths where Blender stores data / scripts after you install them.

https://docs.blender.org/manual/en/dev/advanced/blender_directory_layout.html?highlight=directory

If you remove Blender from all those places, and then reinstall, you'll be ready to rock again.

__

Blender, like almost all programs, must store persistent information like preferences, themes and scripts somewhere on your hard-drive. This is information you don't want to lose when you update Blender to a newer version. Normally that's exactly what you want, but if the stored information contains some weird content ( like in your case ) you can do a purge by removing all references to Blender from the directories listed in the link above. Blender will add those directories back again if it needs to.